1. Field of the Invention
The present invention is related to an electrical socket, and more particularly to a zero insertion force (ZIF) socket for electrically assembling an integrated circuit chip to a printed circuit board (PCB), wherein the ZIF socket has an actuation member for motivating a cover relative to a base thereof.
2. Description of Related Art
ZIF sockets are widely used in computer industry for electrically assembling a central processing unit (CPU) component to a printed circuit board. The ZIF socket usually comprises a cover defining a plurality of upper passageways therein and slidably engaging with a base having a corresponding number of lower passageways retaining contacts therein. The ZIF socket further includes an actuation member for moving the cover with respect to the base and the actuation member has an operating lever and a cam shaft providing a cam member. When the operating lever is oriented vertically to the base, the pins of the CPU component can be freely inserted into the socket. Successively, the operator manually pushes the operating lever downward to a horizontal position, during which the cam member moves the cover together with the CPU component horizontally and the pins of the CPU component are moved to engage with the corresponding contacts in the base. Reversely, when the operating lever is moved from the horizontal position back to the vertical position, the cover together with the CPU component is moved horizontally in a reverse direction. Therefore, the engagement between the contacts of the socket and the pins of the CPU component is released, and the CPU component can be detached from the socket.
U.S. Pat. No. 6,280,223 discloses such a ZIF socket having an actuation member. Referring to FIG. 5, the actuation member 30xe2x80x2 includes a cam shaft 32xe2x80x2 and an operating handle 31xe2x80x2 perpendicularly extending from the cam shaft 32xe2x80x2. The cam shaft 32xe2x80x2 has a cam member 33xe2x80x2. The cam member 33xe2x80x2 has a driving side 330xe2x80x2 for driving a cover of the socket to move with respect to a base thereof and a plane side 332xe2x80x2 opposite to the driving side 330xe2x80x2. The driving side 330xe2x80x2 is a slope plane and includes a start portion 3300xe2x80x2 at one end thereof and an end portion 3302xe2x80x2 at the other end thereof. From the start portion 3300xe2x80x2 to the end portion 3302xe2x80x2, the distance between the driving side 330xe2x80x2 and the plane side 332xe2x80x2 of the cam member 33xe2x80x2 is the same. Referring to FIG. 6, when the operating handle 31 xe2x80x2 is oriented in a zero degree position, that is, the socket is in an open position, a displacement of the cover relative to the base is zero and accordingly a contact stress between the cam member 33xe2x80x2 and a cover plate of the cover is zero. With the operating handle 31 xe2x80x2 rotated towards its final position continually, both the displacement of the cover relative to the base and the contact stress increase gradually following the increase of the rotated angle of the actuation member 30xe2x80x2. Therefore, when the socket is in a closed position, the displacement of the cover relative to the base is maximal, accordingly the contact stress between the cam member 33xe2x80x2 and the cover plate of the cover arrives at a top peak. The cam member 33xe2x80x2 is made of zinc alloy. When the socket is exposed to an elevated temperature due to the operation of the CPU component mounted on the cover, the high contact stress causes the cam member 33xe2x80x2 to creep because of the poor creep strength of zinc alloy. The creep of the cam member 33xe2x80x2 causes the cam member 33xe2x80x2 to deform from its original configuration whereby the cam member 33xe2x80x2 can no longer achieve its requested stroke when it is rotated to move the cover relative to the base. Accordingly, the pins of the CPU component can not be moved to correctly engage with the contacts in the closed position or totally disengage from the contacts in the open position of the socket.
Hence, it is requisite to provide an electrical socket with an improved actuation member to overcome the above-mentioned disadvantages.
Accordingly, the object of the present invention is to provide an electrical socket having an improved actuation member which can provide an effective stroke for the socket to ensure a reliable connection between the pins of an integrated circuit chip and conductive contacts of the socket.
In order to achieve the object set forth, a ZIF socket in accordance with the present invention is adapted for supporting an integrated circuit chip on a circuit board. The socket comprises a dielectric base defining an array of terminal passageways, a plurality of conductive contacts received in the terminal passageways, a cover slidably mounted on the base and an actuation member assembled between the cover and the base for moving the cover with respect to the base. The base defines a receiving chamber in a top surface thereof. The actuation member includes a cam shaft received in the receiving chamber and having a cam member for moving the cover with respect to the base. The cam member provides a driving side having a scraggy surface, and a plane side opposite to the driving side. The driving side comprises a start portion at one end thereof, an end portion at the other end thereof, and a tip portion between the start portion and the end portion. From the start portion to the end portion of the driving side, the distances between the driving side and the plane side are different. The distance from the tip portion of the driving side to the plane side is a maximum distance, while the distance from either the start portion or the end portion of the driving side to the plane side is smaller than the maximum distance, whereby a contact stress between the cam member and a cover plate of the cover is released when the socket is in a closed position.